Numerous devices are known for screwing on caps, and in particular a device comprising a gripping head fixed to a rotary spindle connected to a drive shaft via a friction clutch whose adhesion limit corresponds to the tightening torque that is to be applied to the caps. Because of the way that type of device operates, the clutch is designed to slip while each cap is being tightened, and that gives rise rapidly to wear on the friction elements, which requires the screwing-on device to be stopped frequently to tighten up the friction elements in order to obtain the desired torque.
A pneumatic device is also known that includes an actuator whose rod carries a rack connected via deflector pinions to a rotary spindle carrying the gripping head. The tightening torque is determined by the feed pressure of the pneumatic actuator and that pressure can be adjusted once and for all for a given cap tightening torque. However, because of the mechanism for deflecting the movement of the rack connected to the pneumatic actuator, that device is voluminous, which limits the number of cap screwing-on devices that can be installed on any one machine.